Welcome to
I've Never Lost the Wonder.

This is a noncommercial site
operated by Max Robinson and
dedicated to passing on and preserving
knowledge of vacuum tube circuits and techniques.

Keep the electrons flowing and the tubes glowing.


Join the Fun with Tubes discussion group.
Now all of you who have been exchanging email
messages with me can communicate with each
other directly. To subscribe send an email to
See you on the list.

Activity Log is Back

Day to day I am doing things that those other than
myself may be interested in. These activities
may or may not wind up on a page of their own
someday. If I become involved in a long project
there may be long periods of apparent inactivity
on this site. This page will let you know what
I am up to in my shop. If you have suggestions
Concerning what I am working on don't hesitate
to make them known to me. To read about my
daily activities click here.

The people who run the website EE Web have
interviewed me and written a very
nice article. Here is the link.
EE Web article.

An Observation.

If I worked on radios the same way doctors worked on people when ever a capacitor, resistor, or tube, failed I would just take it out and throw it away. Yet the radio would be expected to work as well as when it was new. So far I am down my tonsils, adenoids, about one and a half feet of large intestine, and a gall bladder. My power output is down and my distortion percentage is up.

Fun With Tubes now has a sister site.
It's called Fun With Transistors.
If you would like to tinker with electronics
But you would rather not poke around among
High voltages, check it out.


An Arduino Based
Audio Power Meter
Announcing a new series of articles.
Equipment Reviews
Two new entries under Test Equipment.
Bench Power Supplies for Tubes
Vacuum Tube Volt-Ohm Meter
Here's some help for anyone trying to build
or just understand these devices.
IF Transformers for New Construction.
Replacement IF Transformers for AA# Radios.
You really can use transistor IF transformers
in tube Circuits if you do it right.
Here's another design from Tim E. Smith.
The sound will surprise you.
I have done for the communications receiver
What I did for the All American Five.
An Intermodulation Distortion Analyzer.
You can build.
Speaker Impedance
Did you know it isn't constant?
Characterizing Transformers
and Interpreting Lead Colors.
The Wise Linearized Williamson Circuit.
Even this classic can be improved upon.
Harman-Kardon A-300
New information has been added
including distortion measurements.
Hotel Radio.
Have you ever seen one like this?
Design Stable
Feedback Loops

Resistors' Behavior
at MF, HF, and VHF.

A resistor may not
always be a resistor.

What do I need to have fun with tubes?
Click here for the answer.

The Basics of Electricity and Electronics.
DC Circuits: Series Circuits, Parallel Circuits, Ohms Law, and Scientific Notation.
AC Circuits: RC, RL, and RLC Networks, Filters.
Vacuum Diodes: Tubes with two elements.
Vacuum Triodes: Adding a grid to the diode.
Tubes with 2, 3, and 5 grids.
Amplitude Modulation (AM), Single Side-band (SSB), and Frequency Modulation (FM)
What is ground? One of the Most Misunderstood Concepts in Electricity.
Transmission Lines and Standing Wave Ratio (SWR): Another Misunderstood Concept.
Test Instruments.
How they work and how to use them.
Bench Power Supply.
Grid Dip Meter (GDM) / Grid Dip Oscillator (GDO).
The Neglected Q Meter.
The Vacuum Tube Volt-ohm Meter (VTVM).
Equipment Reviews
I have decided it would be helpful to viewers of this page
if I post reviews of currently manufactured test equipment.
I have not been given any of this equipment in exchange for
a favorable review. Nor did I receive any discount other than
what the dealer makes available to all customers. I do this in
the hope that I may save you from buying something that
doesn't meet your needs.
Hantek® Model DSO5202P Digital Sampling Oscilloscope
SIGLENT® Model SDG810 Function Generator
How To Do It.
Restoring Electrolytic Capacitors that Appear to be Dead.
Testing Capacitors: Do You Really Know How?
Characterizing Transformers and Interpreting Lead Colors
Reading Resistor and Capacitor Color Codes
Soldering and Unsoldering
Eliminating Ground Loops
Links to Pages on Designing and Building Speakers
Tips From Mac's Workbench
Construction Projects
When I retired in 2001 I was looking forward to building
all those things I had put off for years. I had accumulated
a closet full of parts and I was going to build things
almost for free. .

Then something called the www came along. As a result
I have spent no small amount of money buying parts that
are currently in production. My reason was to make it easy
to duplicate the project. Most people who build these items
are clever, knowledgeable, and web wise. Therefor I am
going to use the free parts I have on hand. I will give
specifications but you are on your own to find equivalent
parts. Where I have bought new parts I will give the source.

Granted, some of the projects below are silicon based.
These are test equipment and in this application, whether
we like it or not, silicon is more stable, easier to build,
smaller, lighter, and performs better, than tubes.

4 Ways to Breadboard: Only One of them is Any Good.
8 Simple Power Supplies For Your Workbench.
Audio Power Meter Has Linear Scale, is Arduino Based.
The Best Breadboard: Soldering Doesn't Take Much Longer and is More Reliable.
Filter Choke Analyzer: Test Filter Chokes Under Current Load.
An IC Socket for Tubes: Not Nearly as Good as it Seemed.
Inexpensive Line Voltage Changer
An Intermodulation Distortion Analyzer.
A Load Box for Testing Power Supplies
Low Resistance Adapter for a Digital Multimeter
Using the Low Resistance adapter to characterize Unmarked Power Transformers
Making AM IF Transformers for New Construction.
Making AM IF Transformers for Replacements in Older AM Radios.
Modifying a Heath IG-18 Audio Generator For Ultra Low Distortion.
PLL Frequency Control For AM Band Receivers. Know Where You Are.
Power Supply & Amplifier: Complex but Very Useful.
Radio and Detector Circuits.
How AM Radio Works: A Simple Description.
How FM and FM Stereo Works
Winding Coils: To Wind or to Buy. Only You Can Answer That Question.
Build a Crystal Set
Build De Forest's Audion: That's Right, You Can Build His First Version of the Audion.
Grid Leak Detector: Needs an Amplifier.
Plate Detector: Needs an Amplifier.
Infinite Impedance Detector: Needs an Amplifier.
Regenerative Detector: Needs an Amplifier.
TRF Receiver: Needs an Amplifier.
Simple Superhet Receiver: Discusses Principles of Mixing and Image Frequencies.
3-Tube Superhet: Needs an Amplifier.
4-Tube Superhet: Needs an Amplifier.
5-Tube Superhet: No Coil Winding, Complete.
The All American Five: There Were Millions Made.
Introduction and Power Supply
The Converter
The Intermediate Frequency Amplifier
The Detector
The Audio Section
Cautions, Precautions, and Troubleshooting
Communications Receivers
Image Rejection, IF Bandwidth, and Number of conversions
Block Diagram
Construction Tips
Power Supply
Audio Amplifier
RF Amplifier and Preselector
Converters, Mixers, and Local Oscillators
IF Amplifiers and Band-pass Filters
AGC (Automatic Gain Control) and S Meter (Signal Meter)
Audio Amplifiers: How They Work
Power and Output Transformers: The Basics.
A Basic Power Supply: Found in the Newcomb D10.
A Technical Discussion of Power Supplies: Not For the Faint of Heart.
Resistance Coupled Amplifier, A Basic Building Block
Magnetic Phono Preamp: With Two Examples.
Volume and Loudness Controls; What the manufacturers don't want you to know.
Tone Controls: From Simple to Complex.
Balance Controls: The Good, the Bad, and the Useless.
Phase Inverters, Split Load Phase Inverters, and Drivers
Push-Pull Outputs
Overall Feedback, Pros and Cons
The FTC and Amplifier Power. Caveat Emptor.
Audio Amplifier Design.
How Much Power is Enough? It Depends.
Speaker Impedance: Did you know it isn't constant?
A Low Distortion Gain Block: Gain from 6.7 to 34, THD less than 0.060%.
How Does Removing the Cathode Bypass Capacitor Affect Distortion.
Practical Tone Controls: Passive and Active.
Phase Inverters and Drivers: The Heart of an Amplifier
The Pentode/Triode as Amplifier/Phase Inverter.
The Wise Linearized Williamson Circuit.
An Amplifier Test Bed: Low THD Driver, Full Metering, & Regulated G2 Voltage.
Experiments with Triode Power Amplifier Circuits.
Designing an Amplifier with Feedback. A Downloadable Program Helps.
How To Design and Optimize Feedback Loops For Best Performance.
Optimizing Feedback Loops, a different point of View. Tim E. Smith.
An Amplifier Smorgasbord: Take Your Choice.
50 Watt Monoblock Amplifier: 6L6 GC.
The 70 Volt Line Amplifier
Contest Winning Amplifier: Results of the 2012 Amplifier Contest.
An EL34 Ultra Linear 50 Watt/Channel Amplifier.
Story of the Original Koss Headphones: Leads Into the Next Project.
A Dedicated Headphone Amplifier
Tim's Second Amplifier
Triode Monoblock: 6L6 GC.
Ultra Linear Monoblock: 6L6 GC.
A Unique Circuit Circlotron Amplifier: Probably Not Worth the Complexity.
Photo Gallery
The Hotel Radio: No Longer a Mystery.
Project Pictures Sent to me by Viewers of this Page.
Schematics of Viewers' Projects.
Tour My Kilowatt AM/SSB Ham Station
Tour My Old Tube hi-fi and Stereo Systems.
The Lawnmower House, The Teddybear Cottage, and My Woodshop.
A New Workbench and Other Revisions to my Electronics Shop.
It Isn't Finished. Work on the Electronics Shop continues.
Operating Instructions
Silvertone Wire Recorder/Phonograph/Radio
MaxCAD Drawing Program Instruction Manual
Restoration Projects
1937 Philco Radio: This Radio Needs a Battery Eliminator to Work.
Heathkit Power Supply: The Fault Was a Most Peculiar Tube.
Harman-Kardon A-300: A Basket Case From eBay Plays Again.
Atwater-Kent Model 20: Restoring a 93 Year Old Radio Isn't Easy.
Useful Information
Verifying My Test Equipment: Making Accurate Measurements is not Easy.
Resistors' Behavior At HF and VHF. When is a Resistor Not a Resistor?
Tube Cross-reference and Selection Guide
Catalogs of Discontinued Parts
Free Programs You Can Download
Other things you can download.
Textbook, Electronics for Non-Engineers
Textbook, Troubleshooting Techniques.
E-mail me

I've Never Lost the Wonder.

As I have said elsewhere on the web I became hooked on electronics when I saw a film on what was then known as educational television which contained animation illustrating how a vacuum tube worked. Memory of the exact year has grown a bit dim but it should have been 1951 or 1952. After that I would look into the back of my radio at night and think about the processes that were going on inside those glowing tubes and a sense of awe and wonder would come over me. The smallest things in nature, as known at that time, were being controlled inside those tubes to capture music from the air and deliver it to the speaker so I could hear it. As I began to understand radio my wonder only increased. I could hear a record that was being played on a turntable more than 1000 miles away as clear as if it were being played on my own phonograph. Actually clearer because the "needle" and record were in much better condition than my own. Over the past 66+ years I still haven't lost that sense of wonder.

It is also true that I have the same feelings about electrons and holes flying around inside the tiny crystal of a transistor. Think of it, I can hold in the palm of my hand a working computer that has more power than those first vacuum tube computers that would have filled a rich man's mansion.

The whole field of electronics encompassing audio, radio and digital systems still motivates and inspires me to wire up circuits. I still feel the same when it all works. I hope to share some of it with you.

Do you like music? I also write songs which are arranged and mixed
so you can understand the words, and the lyrics are worth listening to.
Take a peek into my right brain. Visit Max's Music Place. Click here.

Email Tube Man.  SHA ZAM!
Everything you always wanted to know about
vacuum tubes but didn't know who to ask.

Ask Tube Man.

Would you like to tinker around with tubes but don't know what to do? Want to fix up that radio that belonged to your great-grandfather but don't know where to start? Are you experienced in working with tubes but you just came across a problem which has you stumped? Tube Man knows all and tells all. Just click on the super hero's picture to email a question to him. See questions submitted to Tube Man and his answers.

Who and What.

This web site is owned and operated, as a hobby, by Max Robinson. As time goes by I will post tutorials on the fundamentals of electricity and electronics, interesting circuits you can build with vacuum tubes and op amps, and I will share some of my experiences restoring antique radios and early electric phonographs.

I have a master's degree in electrical engineering from the University of Florida 1966. My early EE classes covered vacuum tubes so I know what I am talking about and doing. If you have any questions or suggestions feel free to email me.

If I Don't Answer...

I scrupulously answer all emails sent to me. If you send me one and you don't hear from me in a reasonable amount of time maybe something went wrong.

On a number of occasions I have received emails from people seeming to be asking legitimate questions. When I attempt to answer them I get back one of those "Mail System Error" messages saying that there is no such address or my email address has been blocked by the sender. Some anti spamming programs are quite strict and maybe you forgot to enter my address as "allowed". Check your anti spam list to be sure my reply will be given to you instead of being bounced back to me.

On the other hand maybe this is someone's idea of juvenile fun. No doubt the people who have done this (you know who you are) think this is very funny. To me it's just a minor annoyance. Even though it's a small thing I could do without it. Just because you're not having fun don't spoil it for the rest of us.

My Favorite things.
  • Old Country Music
  • Old Rock-n-Roll
  • Folk Music
  • Classical Music
  • Old Radios
  • Old Records
  • Old Record players
    Gramophones, Victrolas, etc.
  • Young Women (Only kidding Sue.
  • One particular woman (age, I'm not telling).

Thank you for visiting my page at Angelfire.
Please come back and visit again!

This site begun March 14, 2001

This page last updated Monday, July 10, 2017.

Web ring has been removed because it was hijacking browsers away from this site into the ring. The ring has been rung.